4 N. ODHNER, NORTHERN AND ARCTIC INVERTEBRATES. VI. PROSOBRANCHIA. 2 SEMIPROBOSCIDIFERA. 



in view of the advantage afforded by having measurements that are adapted to the main 

 form of the shell, they expressing most exactly the formål variation. 



In the family Lamellariidoe, where the morphology of the soft parts of the animal 

 is the point of principal systematic import, some contributions to the anatomical struc- 

 ture have been given, as this matter appeared to have been insufficiently dealt with in 

 the literature of the subject. For the rest no anatomical investigations have been made, 

 except those of the radula, which were undertaken in order that its variation might be 

 stated. 



With a view of illustrating the accounts of the variation, several complete series 

 of shells have been figured on the plates. These are from photographs copied on East- 

 man's platino-bromide paper and afterwards retouched; Plate 2 has been particularly 

 carefully and very skilfully retouched by Herr G. Liljevall, the artist, who has also 

 delineated Figures I — 6 of Plate 5, illustrating details of Otichidiopsis. 



I 



